1. Field of the Invention
The present general inventive concept relates to a housing assembly of an organic photoconductive (OPC) unit, and in particular, to a housing assembly to protect an OPC drum on which an image to be printed is formed in an image forming apparatus.
2. Description of the Related Art
In general, an image forming apparatus, such as a copying machine, a printer, or a combined machine, is used for forming an image on an OPC medium and then printing the image on a recording medium. For example, a laser printer prints an image on a sheet of paper through a series of steps, e.g., forming a desired image on an OPC medium with a laser scanning unit (LSU) and then transferring a developed image onto a paper through an image transfer unit.
Such an image forming apparatus requires an OPC unit including an OPC medium for forming an image. For a mono-printer, a housing assembly of the OPC unit is typically formed in an integral structure to enclose not only an OPC drum but also a developing roller or the like.
A conventional housing assembly 10 of an OPC unit is described with reference to FIG. 1 by way of an example. The housing assembly 10 includes a main opening 14 through which an OPC drum 22 projects, and a sub-opening 12 that serves as an exposure window.
As shown in FIG. 1, the housing assembly 10 entirely protects toner, a toner stirrer 16 for supplying the toner, a toner feeding roller 18, a developing roller 20, an electrification roller 24, and an OPC drum 22.
The toner feeding roller 18 serves to transfer the toner to the developing roller 20 and is located adjacent to the developing roller 20, and the developing roller 20 is in contact with the OPC drum 22 with a developing nip or gap being formed between the developing roller 20 and the OPC drum 22, so that the developing roller 20 develops an image formed by a laser scan unit 26 with the toner received from the toner feeding roller 18 to form a developed image on the OPC drum 22.
As shown in FIG. 1, in general, the conventional housing assembly 10 is provided with a toner storage case 13 positioned higher than any of the developing roller 20 and the toner feeding roller 18, so that the toner can be moved by weight toward the developing roller 20 through the toner feeding roller 18.
However, such a housing assembly 10 for a mono image forming apparatus has a disadvantage in that it can not be employed in a color image forming apparatus provided with four respective color developers each for yellow, magenta, cyan and black.
In particular, in a color image forming apparatus of a multi-path type including one OPC medium and one image transfer medium, the OPC medium is developed while individually coming into contact with each developing unit in a state that a developing nip or gap is formed between the OPC medium and the developing unit. Therefore, it is not possible to employ such a construction of the conventional housing assembly that has been used in the conventional mono image forming apparatus provided with an developing roller, etc., in the color image forming apparatus, and it is required to develop a new housing assembly according to a novel concept.
Although a currently developed color image forming apparatus uses a hard type OPC drum, which is not a belt, it has to have a plurality of small-diameter OPC drums for colors and also a plurality of color developing units corresponding to the OPC drums. In the currently developed color image forming apparatus, an image is developed by the respective color developing units and transferred to a big-sized transfer belt from the respective OPC drums. Such a color image forming apparatus with the above construction is bulky and is manufactured at high costs.
In order to the solve the above problem, a method has been suggested, in which a plurality of movable developing units selectively contact one single small-diameter OPC drum one by one to develop a color image. However, this method has a problem of an unstable developing process because of the movable developing units, thereby losing reliability of a developing quality.
Alternatively, another method also has been suggested, which uses an OPC belt instead of the OPC drum. According to this method, a developing process is performed in a manner that respective color developing units are brought into contact with the OPC belt. However, it is difficult to maintain a constant tension of the OPC belt, and the OPC belt becomes loosened when being used for a predetermined time or a tension of the OPC belt attenuates, thereby causing a poor contact with the developing units.